Asphalt-based roofing materials, such as roofing shingles, roll roofing and commercial roofing, are installed on the roofs of buildings to provide protection from the elements, and to give the roof an aesthetically pleasing look. Typically, the roofing material is constructed of a substrate such as a glass fiber mat or an organic felt, an asphalt coating on the substrate, and a surface layer of granules embedded in the asphalt coating.
A common method for the manufacture of asphalt shingles is the production of a continuous sheet of asphalt material followed by a shingle cutting operation which cuts the material into individual shingles. In the production of asphalt sheet material, either a glass fiber mat or an organic felt mat is passed through a coater containing hot liquid asphalt to form a tacky, asphalt coated sheet. Subsequently, the hot asphalt coated sheet is passed beneath one or more granule applicators which discharge protective and decorative surface granules onto portions of the asphalt sheet material.
In the manufacture of colored shingles, two types of granules are typically employed. Headlap granules are granules of relatively low cost used for the portion of the shingle that will be covered up on the roof. Colored granules or prime granules are of relatively higher cost and are applied to the portion of the shingle that will be exposed on the roof.
Colored granules are typically colored with a ceramic coating at a granule quarry and transported to a shingle manufacturing facility. Colored granules from different granule quarries are not used interchangeably at shingle manufacturing facilities. The colored granules from different granule quarries are not interchangeable because shingles made therefrom do not appear identical to the customer when used side-by-side on a roof.
To provide a color pattern of pleasing appearance, the colored portion of the shingles may be provided with areas of different colors. Usually the shingles have a background color and a series of granule deposits of different colors or different shades of the background color. A common method for manufacturing the shingles is to discharge blend drops onto spaced areas of the tacky, asphalt coated sheet. Background granules are then discharged onto the sheet and they adhere to the tacky, asphalt coated areas of the sheet between the granule deposits formed by the blend drops. The term “blend drop,” as used herein, refers to the flow of granules of different colors or different shades of color (with respect to the background color) that is discharged from a granule blend drop applicator onto the asphalt coated sheet. The patch or assemblage of the blend drop granules on the asphalt coated sheet is also referred to as the “blend drop.”
The apparatus for depositing granules onto the asphalt coated sheet is referred to as a blender, which can be comprised of a series of hoppers positioned to drop granules onto the sheet. In a typical blend drop shingle operation, the blender includes four hoppers that periodically deposit blend drops of granules of four different shades. The blender also includes a fifth hopper that drops background granules on the areas of the asphalt coated sheet that have not been covered by granules from the first four hoppers.
Various types of granule dispensing hoppers are known for use in granule blenders. One type of dispensing hopper is a fluted roll. Another type is a pneumatically assisted and controlled hopper as disclosed in U.S. Pat. No. 5,520,889 to Burton et al. Since the manufacture of shingles is carried out at high, continuous line speeds of hundreds of feet per minute, coordination and timing for the granule deposits from the various hoppers is imperative. The blender is usually operated by an electronic blender controller that provides signals to the various granule hoppers to impart the proper sequencing and duration of the blend drops of each blend drop color, and of the background color.
The various shades or colors of granules in each of the hoppers are typically created by mixing colored granules of different colors from several different supplies of granules, each of which is a pure or single color. For example, the first blend drop may be made by mixing three parts pure brown granules and one part pure black granules. The second blend drop may be made by mixing four parts pure brown granules and two parts pure white granules. Other combinations may be used for the third and fourth blend colors. The fifth hopper may contain background granules that are a color reflecting a combination of the granules from the first four hoppers.
One of the problems associated with the manufacture of shingles with blend drops is that the shade or color can deviate from the designed shade or color, and therefore be out of specification. This can occur because of mixing of colored granules from different granule quarries. Sometimes defects or variations in shades or colors cannot be detected during the manufacturing of the shingles. In such cases, the defect may not be discovered until the shingles are actually installed on a roof. As a result, shingle manufacturers often implement do not mix programs, wherein shingle manufacturing facilities are instructed not to mix like-colored granules from different quarries, and shingle customers are instructed not to mix shingles produced at different manufacturing facilities and/or on different production lines. It would be advantageous if there could be developed an improved system for manufacturing colored shingles.